Electrolytic device and method of making same



-Mmh 3,1, 1942. J', B BRENNAN Y. 2,278,161

ELECTROLYTIC DEVICE AND METHOD 0F MAKING SAME Filed Oct. 2, 1939 @VEN-ron` l.ms/vw B. Bief/WAN BY U-IE,{

ATTORNEYS Patented Mar. 43l, 1942 'UNITED STATES PATENT OFFICE LECTBOLYTIC DEVICE AN D METHOD F MAKING SAME .y Joseph B, Brennan, Euclid, Ohio,

n Application October 2, 1939, Serial No. 297,507

12 Claims.-

plied to other types of electrolytic devices and to electrodes composed of other materials.

`As pointed out in my copending application noted above electrolytic devices such as electrolytic condensers embodying one or more electrodes made up of accumulations or masses of fine metallic filaments, strands, orrbers, preferably intertwined, flted, bundled, bound, or. matted electrical contact between the conductors andthe filaments making up the metallic wool.

Heretofore it has been a quite'general ypractice l in the art to employ only aluminum oi' very high vpurity (for example, 99.8% pure) in the manufacture of filmed electrodes for electrolytic condensers. My invention not only contemplates the manufacture of electrodes from'such high purity aluminum, but also contemplates the production of filmed electrodes fromy Ametallic wool composed `of aluminum of lesser purity or ofk aluminum alloysnand having the characteristics of low leakage and freedom from contamination ordinarily only lfound in electrodes of very high purity aluminum. When the metallicrwool is made of an aluminum alloy such as "2S for example, or of ordinary commercialv aluminum, the

together in the form of masses, mats or pads of metallic wool are highly advantageous in that in such form a small weight of metal has a very Y extended surface area. The result is that a condenser embodying such an `electrode has a high capacity per unit of electrode mass and further such a condenser can be of compact form and can be economically manufactured.

The present invention relates to velectrodes of this general type, i. e., constructed of metallic wool, and it is among the objects of this invention to provide an improved metallic wool electrode of very low resistance and of high efficiency.y

Another object is to provide electrodes, and particularly filmed electrodes, manufactured of aluminum alloys and which will have the desirable characteristics heretofore obtainable only with electrodes made of extremelyhigh purity aluminum.. A further object is to provide electrodes composed of metallic wool having increased effective surface area and capacity..

Briefly my present invention contemplates, in

one of its aspects, the production of electrodes for electrolytic condensers from masses, mats or pads of metallic-wool such as aluminum wool, the mats or pads being provided with one or more additional conducting members such as strips of foil or wires which are arranged to distribute the i current throughout the condenser so that many of the strands, fibers or filaments of the metallic wool electrode are directly connected to such a conductor while substantially all of the filamentsv are in low resistance electrical circuit therewith, with the result that substantially all of the .iliaments operate eiiiciently, the resistance of the electrode as a whole vis reduced, and its eiiiciencyi is increased. Preferably the individual filaments and the conductors are intimately bonded to each v other as by welding or' metal spraying. In any event a connection is made that will `insure good in that patent to increase the surface area of aluminum and vto remove surface impurities therefrom. However, in the case of aluminum wool the etching operation has an effect different from its effect on other materials such as aluminum foil or rods. In conjunction with the etching of aluminum foil or rods, it is desirable to use aluminum. of the highest possible purity even though the .etching operation does apparently operate to remove many of the surface impurities. However, according to my present invention aluminum alloys and aluminum of lesser purity can be employed with excellent results, the reason being, I believe, that the aluminum wool has such an extended surface areak in comparison with its mass that the etching of the surfaces and apparent removal of the impurities from the surfaces of the fine filaments of the metal functions, in my opinion, to remove substantially all of the impurities from the entire mass of metallic'wool. Whatever the reason may be, the result is that etched electrodes composed-of aluminum alloy wool -have excellent leakage characteristics and have the characteristics of durability and long life which heretofore have been obtained only by the use of electrodes made from aluminum of exceptionallyhigh purity. Of course-the etching operation can also be applied to electrodes composed of aluminum wool of high purity, in which case the principal result is an increase in the capacity of the electrode. l y

Referring to the drawing,l Figure l is a sectional view through a paste type of condenser embodying my invention; Figure 2 is a plan view of an electrode Asuitable for use in a condenser such' as that illustrated in Figure l; Figure 3 is a sec-v` An electrolytic condenser embodying apreferred form of my invention may take any convenient or conventional form and as shown in Figure l, may comprise a suitable box or container I having electrodesil, I2, Il and I4 therein, the electrodes being separated from each other by suitable spacers I5, I6, and I1. Alternate electrodes are connected to a common terminal or lead, that is electrodes II and I3 are connected to terminal while electrodes I2 and I 4 are connected to terminal 2|. The electrodes are pads or mats of metallic wool composed of a film forming metal such as aluminum. Both sets of electrodes are composed of such material and both are provided with dielectric lms in a condenser intended for alternating current service. However, in a condenser intended for direct current service, only the electrodes comprising the anode need be dielectric filmed. The cathode in such a condenser may be of non-filming material such as copper, or if composed of aluminum filaments or aluminum foil the surfaces o( the filaments or foil need not be lmed.

The flneiilaments or threads of metal making up the pads may be produced by methods known to those skilled in the art for example by cutting ofi' fine shavings from a metallic bar or tube, Preferablythe filaments are of irregular cross vsection or at least are not round so thateach filament will have a greater area per unit of mass than would be the case if the filaments were of round cross section. The filaments are all preferably very fine, the minimum cross sectional dimension being vnot greater than .005". In producing the filaments I prefer to employ a cutting oil or coolant which is maintained at a low temperature, preferably below 40 F. If the filaments are cut from a tube the coolant may be circulated through the interior of the tube during the cutting operation to further cool the material. of kerosene and lard oil. for example, as a coolant and I find that by artificially cooling the oil the life of the cutting tools is prolonged and it is possible to produce filaments of greater length 2,095,666 being suitable. ,As those skilled in the art will appreciate, other suitable electrolytes may be employed. v

The steps of forming the nlmand impregnating the electrodes with electrolyte are known to the art as applied to other types of electrodes and these steps per se form no part of my present invention which relates particularly to the electrodes. As shown'in Figures 2 and 3, a suitable electrode in which efficient use is made of substanti'ally` all of the metal making up the electrode may comprise. apad of aluminum wool 25 having a conductor 26 extending longitudinally thereof and having an end portion projecting beyond the pad and constituting part of the terminals 20 or 2| shown in Figure 1. Preferably the conductor extends throughout the length of the pad and is crossed at intervals by supplementary transversely extending conductors 21. To insure a, low resistance path for the flow of current from -the terminal to substantially every part of thepad the conductor 26 is welded to the pad through substantially its entire length, preferably by closely spaced electric spot welds 28 indicated diagrammatically on the drawing. Further, the transversely extending conductors 21 are Similarly welded to the conductor 2B and to the fibers or filaments of the pad with the result that many, if not substantially all, of the filaments are connected directly to a conductor and thus current may be distributed to the entire pad and substantially all I may use a mixture than can be produced by ordinary cutting methods.

The extensive surface of the filaments or strands may be provided -with dielectric nlms in any desired manner known to those skilled` in the art. For example, the electrode may be subjected to electrolysis as an anode in a suitable lm forming electrolyte such as a solution of borax and borlc acid. The film forming operation is continued until the leakage current is reduced to the desired low value at the maximum forming voltage, which is ordinarily somewhat in excess of the voltage for which the condenser is designed. Condensers of this type may be operated successfully under relatively high voltages, i. e., voltages of the order of 500 or 600 volts.

In condensers of the type illustrated in Figure i the electrodes are preferably' impregnated with a suitable viscous or pasty film maintaining electrolyte, the urea formaldehyde electrolyte describedl and claimed in my Patent No.

of the filaments through short, low resistance paths, `thus resulting in alow resistance electrode which will operate very eliiciently.

. In Figures 4 and 5 I have shown a modified form of electrode .embodying a ypad 35 and a longitudinally extending conductor 36 generally similar to the pad 25 and conductor 26 described above. However, in this modification the transverse conductors 31 comprise wires stitched through the pad and through the conductor 36 as shown particularly in Figure 5. To further increase the yconductivity of the assembly the wires are preferably Welded to the conductor 36 and to the pad 35 by spot welds 38. In this type of electrode, as in that previously described, the conductors 36 and 31 provide short, low resistance paths for the fiow of current through the electrodes, and the stitched conducting wires 31 further function to compress and bind together the fibers or filaments of the pad. 'I'his construction is particularly advantageous in conjunction with mats or pads of metallic wool in which the fibers or filaments have been combed or straightened so that they extend generally parallel to eachother longitudinally of the pad. In such a construction the stitching functions to bundle or bind Vthe filaments together as well as to furnish'highly conductive pathsV to the individual iilaments.

A further modification is illustrated in Figures 6 and 7 wherein ythe electrode .comprises two contiguous pads l5 having longitudinally extending conductors 6v and transverse conductors 41 disposed between the pads.4 In this instance the pads are bound together by'spraying finely (iivided molten metal cin andy throughl the pads. the spraying operationv preferably being carried out from both sides and in the manner described `in greater detail in my prior Patent No.' 2,104,010.`

dated January 4, 1938. The finely divided pai'- ticles of metal, indicated diagrammatically '1t 4l, penetrate the porous pads and effectively bind the pads together and electrically and meamarsi l chanically bond the conductors to the pads. Further the ilnely divided sprayed particles function asnoted in my copending application Serial No. 275,481 to increase the effective area of the electrodes and thus further to increase their capacity. As those skilled in the art will appreciate the spraying operation can be applied to the electrodes shown in Figures 1 to 4 if-desired in substitution for or in conjunction withthe welding and if desired a construction embodying two pads such as that shown in Figures 6 and 'l can be bound together by spot vwelding in the manner described in conjunction with the electrodes shown in Figures 2 to 5.

As described elsewhere in this specification, the aluminum wool may be made of substantially pure aluminum, i. e., aluminum of 99.8% purity or better, or commercial aluminum or aluminum alloys can be employed such as the well-known 2S alloy. The conductors utilized with aluminum wool electrodes are preferably composed of substantially pure aluminum. In case an alloy or commercial aluminum is used it is desirable that the aluminum wool be etched, preferably by means of an acidined salt solution as described in my prior Patent No. 2,154,027 to increase the effective area of the electrode and to substantially remove impurities therefromv as described above. y

The etching operation can be also used in conjunction with electrodes made oi pure aluminum. The electrodes may be sprayed with nely divided molten particles of metal, preferably of the same metal as the electrodes are made, in order to further increase their capacity.

The vspraying operation can be carried out in conjunction with etched electrodes if desired, or if desired, the etching operation can be applied to electrodes which have been sprayed with molten metallic particles, thus further increasing the effective area of the electrodes.

In the foregoing specification I have described preferredforms of my invention as applied to a particular type of electrolytic device. Those skilled in the art will appreciate that my invention may be modified in various ways and of said main conductor, and making electrical contact therewith, said conductors of strips or metallic foil welded to said pad.

3. An electrode for electrolytic devices com prising a mat of metallic wool, a conductive wire extending along said mat and stitched and welded thereto, and means for connecting said wire to an external circuit.

4. An electrode for electrclytic devices com-w prising two contiguous mats of metallicywool,

a conductor disposed between said mats, said f l face area'thereof.

- 7. In an electrolytic condenser, a film maintaining electrolyte, an electrode in contact therewith comprising a mat oi.' metallic wool commay be adapted to other types of electrolytic devices, all without departing from the spirit and scope thereof. Therefore it is to lbe understood that my patent is not limited to the em.. bodiments oi' my invention described herein or in any manner other than by the appended claims when given the range of equivalents to s which my patent may be entitled.

I claim: 1. An electrode for electrolytic devices comprising a mat ofmetailic wool composed of nlmforming metalahavlng a main auxiliary conductor extending therealong and a plurality of conductors extending transversely of said main conductor,- and making electrical contact therewith and bonded thereto at a plurality of points intermediate the ends of the mat, said conductors being directly in eilective electrical contact with substantially all of the illaments comprising the mat. 3

2. An electrode for electrolytic devices comprising a mat of metallic wool having amain` auxiliary conductor 4extending therealong and a plurality of conductors extending transversely posed `of nlm-forming metal having minute spray-deposited particles oi' nlm-forming metal adhering thereto. I 8. An electrode VYfor electrolytic devices comprising a mat of metallic wool having an auxiliary conductor comprising a vstrip of thin metallic foil extending therealong and bonded to a substantial number oi' the filaments comprising the mat by spray deposited metallic partieles.

9. An electrode for electrolytic devices comprising a mat of metallic wool having an auxiliary conductor extending therealong and bonded to a substantial number of the iilaments comprising the mat by spray deposited metallic particles adhering to the illaments and to the conductor.

10. An electrode for electrolytic devices comprising a mat of metallic wool having a main auxiliary conductor extending therealong and a plurality of conductors extending transversely of said main conductor andbonded thereto and making electrical contact therewith. said transverse conductors consisting of wires stitched to said mat. y

11; An electrode for eiectrolytic devices comprising a mat of metallic wool, a conductive wire extendingv along said mat and stitched thereto, and means for connecting said wire to an external circuit.v

12. An electrode for electrolytic devices comprising a Imat of metallic wool having a/main auxiliary conductor extending therealong 'and a plurality of conductors extending transversely of said mainconductor, Aand making electrical contact therewith, said conductors electrically and mechanically `bonded t0 a substantial number of the iilaments comprising the mat by spraydeposited metallic particles adhering to said conductors and said illamen f JOSEPH B. BRENNAN. 

